Gigagbyte GA-EP45-UD3P atx 12v 2x4 Problems

[iananan]

A new Build in an antec sonata III 500, with stock PSU, when the atx 2x4 is plugged in, the computer beeps a PSU error at me, when i plug the atx 2x2 pin one in in it's place (on one half only, it can only go on one side) the CPU won't power up and all i get are fans spinning and beeping. without anything plugged in there, fans spin up, but the CPU won't.

what the hell is this thing's problem. it booted to BIOS once, and once only, when we came back with a windows 7 install disc 20 minutes later it wouldn't work. please help.

 

[iananan]

and i'm aware it might just be terrified of windows.

i've done fairly extensive googling on the subject, and the only responses i've found are that the person's power supply didn't actually have a 2x4 pin thing, and this PSU definitely does.

is there a chance that the PSU somehow suffered a major fault in the time it took to walk to a different house and pick up a cd?